a member of the Sacred College of Cardinals, whose duties include electing the pope, acting as his principal counselors, and aiding in the government of the Roman Catholic church throughout the world. Cardinals serve as chief officials of the Roman Curia (the papal bureaucracy), as bishops of major dioceses, and often as papal envoys. They wear distinctive red attire, are addressed as “Eminence,” and are known as princes of the church.

Scholars have disagreed about the origin of the title. There is, however, tentative consensus that the Latin word cardinalis, from the word cardo (“pivot” or “hinge”), was first used in late antiquity to designate a bishop or priest who was incorporated into a church for which he had not originally been ordained. In Rome the first persons to be called cardinals were the deacons of the seven regions of the city at the beginning of the 6th century, when the word began to mean “principal,” “eminent,” or “superior.” The name was also given to the senior priest in each of the “title” churches (the parish churches) of Rome and to the bishops of the seven sees surrounding the city.

By the 8th century the Roman cardinals constituted a privileged class among the Roman clergy. They took part in the administration of the church of Rome and in the papal liturgy. By decree of a synod of 769, only a cardinal was eligible to become pope. In 1059, during the pontificate of Nicholas II (1059–61), cardinals were given the right to elect the pope. For a time this power was assigned exclusively to the cardinal bishops, but the third Lateran Council (Lateran Council) (1179) gave back the right to the whole body of cardinals. The cardinals were granted the privilege of wearing the red hat by Innocent IV (1243–54) in 1244 or 1245; it has since become their symbol.

In cities other than Rome, the name cardinal began to be applied to certain ecclesiastics as a mark of honour. The earliest example of this occurs in a letter sent by Pope Zacharias (Zacharias, Saint) (741–752) in 747 to Pippin III (Pippin I) (the Short), ruler of the Franks, in which Zacharias applied the title to the priests of Paris to distinguish them from country clergy. This meaning of the word spread rapidly, and from the 9th century various episcopal cities had a special class among the clergy known as cardinals. The use of the title was reserved for the cardinals of Rome in 1567 by Pius V (Pius V, Saint) (1566–72), and Urban VIII (1623–44) granted them the official style of Eminence in 1630.

The Sacred College of Cardinals, with its structure of three orders (bishops, priests, and deacons), originated in the reform of Urban II (1088–99). These ranks within the college do not necessarily correspond to a cardinal's rank of ordination; e.g., the bishop of a diocese such as New York City or Paris may be a cardinal priest. From the time of the Avignon papacy (1309–77), the question of the lack of internationality in the College of Cardinals became an increasingly important one; a reform under Sixtus V (1585–90) attempted to provide for it. The question continued to be raised at various times, particularly in the second half of the 20th century.

The cardinal bishops are the successors of the bishops of the sees just outside Rome. There were seven of these sees in the 8th century, but the number was later reduced to six. Prior to 1962 each of the cardinal bishops had full jurisdiction in his own see; since then, however, they preserve only the title without any of the functions, which passed to a bishop actually resident in the see. In 1965 Paul VI (1963–78) created cardinals from among the Eastern Catholic patriarchs and arranged that they should become cardinal bishops on the title of their patriarchal sees.

The second and largest order in the College of Cardinals is that of the cardinal priests, the successors of the early body of priests serving the title churches of Rome. Since the 11th century this order has been more conspicuously international than the orders of cardinal bishops and deacons, including the bishops of important sees from throughout the world.

The cardinal deacons are the successors of the seven regional deacons. By the 10th–11th century there were 18 deaconries in the city, and the reform of Urban II assigned a cardinal deacon to each of them. Originally, the order was limited to those who had advanced no further than the diaconate. Later legislation prescribed that a cardinal deacon be at least a priest. John XXIII (1958–63) and Paul VI, after appointing cardinal deacons who were not bishops, immediately consecrated them bishops.

The pope alone appoints or creates cardinals in the three orders of cardinal bishop, cardinal priest, and cardinal deacon—all of whom are bishops in accordance with the ruling of John XXIII—by announcing their names before the College of Cardinals in a private consistory (a meeting of ecclesiastics, especially the College of Cardinals, for the administration of justice and other business). These newly named cardinals then receive the red biretta and the ring symbolic of the office in a public consistory. Sometimes the pope appoints cardinals in pectore (Latin: “in the breast”), without declaring their names; only when the name of a cardinal in pectore is revealed does he assume the rights and duties of the office.

In 1586 Sixtus V fixed the total number of cardinals at 70, of whom 6 were cardinal bishops, 50 were cardinal priests, and 14 were cardinal deacons. In 1958 John XXIII eliminated the restriction of 70, increasing the number of cardinals to 87, and since then the number has reached more than 100.

Under the influence of the Second Vatican Council (Vatican Council, Second) (1962–65) and in recognition of the need for greater internationalization of the College of Cardinals, Paul VI and John Paul II (1978–2005) appointed many new cardinals; under Paul there were 145 cardinals, and under John Paul there were 185, nearly all of whom had been appointed by him. The growth of the college, however, prompted the imposition of new restrictions on the cardinalate. In 1970 Paul VI directed that cardinals who reach age 75 are to be asked to resign, and those who do not resign are to relinquish the right to vote for a pope when they reach age 80. Paul further decreed that the number of voting cardinals be limited to 120. This restriction was confirmed during the pontificate of John Paul II. In 1996 a new set of rules issued by John Paul provided that, under certain circumstances, the long-required majority of two-thirds for election of a pope could be superseded by a simple majority. John Paul's successor, Benedict XVI, however, restored the traditional requirement of a two-thirds majority in 2007.

One of the most popular, widespread, and abundant of the North American birds, the northern cardinal (Cardinalis cardinalis) is the only red North American bird with a crest. It is the official bird of seven eastern U.S. states and is especially common in the Southeast. The bird has been introduced into Hawaii, southern California, and Bermuda. Males are bright red with a black mask and orange beak. Females are duller red or brown. Thanks to bird feeders, where it favours sunflower seeds, this species has recently expanded its range as far north as southwestern Canada. Both males and females whistle year-round. A pair may raise up to four broods a year.

The desert cardinal (C. sinuatus) is common to the thorn scrub of the American Southwest. Less showy than the northern cardinal, this gray bird with a red mask is also called pyrrhuloxia (formerly part of the bird's scientific name, combining the Latin name for the bullfinch with a Greek reference to the strongly curved, stubby bill). It often forages in small flocks.

Other cardinals belong to the genus Paroaria. The red-crested cardinal (P. coronata), also known as the Brazilian cardinal, has a red head, a white belly, and gray wings. Though native to Brazil, Argentina, Paraguay, Uruguay, and Bolivia, it occasionally can be seen visiting the eastern coast of the United States. It was introduced to Hawaii in 1928 and is now common on the island of Oahu. Because of its beauty and melodious song, it is often trapped for the cage-bird trade.